Extruder (1) for a 3D printer, comprising at least one outer nozzle (2) and a conveying worm (3) for feeding liquid and/or plasticized starting material (4) into the interior chamber (21) of the outer nozzle (2), wherein an inner nozzle (5) is arranged in the interior chamber (21) of the outer nozzle (2), wherein the interior chamber (51) of the inner nozzle (5) is connected to the interior chamber (21) of the outer nozzle (2) via at least one duct (52, 52a, 52b) which is continuous for the starting material (4), and wherein the inner nozzle (5) is mounted such that it can be moved linearly along the longitudinal axis (2a) of the outer nozzle (2). A 3D printer (100) having the extruder (1) and means (8) for generating a relative movement between the extruder (1) and a construction surface (101), on which the object (102) to be manufactured is produced.